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Method and apparatus for pumping out the liquid in a container

Method and apparatus for pumping out the liquid in a container description/claims

The present invention relates to a method and an apparatus for pumping out the liquid contained in a drum, a pail, or another container, by pumping up and discharging the liquid, with a follow plate in airtight contact with the inner peripheral surface of the container. The liquid ranges between high-viscosity liquid and low-viscosity liquid that borders on water. The high-viscosity liquid may be food material, printing ink, sealant, or putty. The food material may be tomato paste or cream.

In general, a method for pumping out the liquid contained in a container open at its top includes mounting a pumping apparatus on a lift for vertically moving the follow plate fitted to a pump, seating the follow plate on the liquid surface in the container, and pumping out the liquid, with the follow plate moving downward with the liquid surface. In general, an apparatus for pumping out the liquid contained in a container open at its top is mounted on a lift for vertically moving the follow plate fitted to a pump. The follow plate can be seated on the liquid surface in the container. The liquid can be pumped out with the seated follow plate moving downward with the liquid surface. Whether the lift moves the follow plate manually or automatically (by an electric motor, an air cylinder, or a hydraulic cylinder), the liquid can be pumped out either with the pump and the follow plate exerting all loads on the liquid surface, or with additional pressure applied on the liquid surface if the liquid is high in viscosity. The follow plate is surrounded by a seal, which may be a rubber ring in the form of a plate, an expandable rubber tube, or another structure, as will be described later on. At least while the liquid is pumped out, the follow plate is lowered with the seal pressed strongly against the inner peripheral surface of the container.

While the pump is pumping out the liquid, the follow plate isolates the inside of the container from the outside (atmosphere), and the pumping action makes the space under the follow plate in the container negative in pressure. When the inside of the container is negative in pressure, the atmospheric pressure presses the follow plate, so that a downward pressure acts on this plate. If the differential pressure is 80 kPa, for example, that for a pail is about 5.1 kN (520 kgf). The load of the pump etc. are further added. Therefore, conventionally, the seal (made generally of rubber) surrounding a follow plate, as stated above, is pressed strongly against the inner peripheral surface of a container so as to prevent liquid leakage. If the follow plate becomes eccentric with respect to the inner peripheral surface of the container, liquid leakage may occur. This makes it necessary to position the container accurately and carefully relative to the follow plate (so that the container can be concentric with the plate).

For example, FIG. 4 shows a follow plate 71 for use in a pumping apparatus of this type. With reference to FIG. 4, an annular rubber ring 72 in the form of a plate is fitted to the outer periphery of the follow plate 71. The outer diameter of the rubber ring 72 is slightly larger than the inner diameter of a container P such as a drum. When the follow plate 71 is inserted into the container P, the air release port 73 is opened for air release. When the follow plate 71 is seated on the liquid T in the container P, the liquid may leak through the air release port 73 and splash, making the environment dirty. This makes it necessary to insert the follow plate 71 carefully into the container P. An on-off valve 74 is connected to the air release port 73. The air release port 73 needs to be closed by operating the on-off valve 74, with the follow plate 71 seated on the liquid T in the container P. The operation is troublesome because it is impossible to observe from the outside of the container P how the follow plate 71 is seated on the liquid T. When the follow plate 71 on the bottom of the container P is lifted, the rubber ring 72 is deformed in close contact with the container, so that the container might be lifted. In order to prevent the container P from being lifted, it is preferable to form an air supply port 75, from which compressed air can be purged through an air injection adaptor 76 so that compressed air can be supplied into the container P. In FIG. 4, reference numeral 2′ indicates a pump body.

FIG. 5 shows a follow plate 81 having another structure, which is surrounded by an expandable rubber tube 82. With the rubber tube 82 contracted, the follow plate 81 can be inserted into a container P. With the follow plate 81 seated on the liquid T in the container P, the rubber tube 82 can be supplied with compressed air through an air supply/release port 83 so as to be expanded. The expanded tube 82 comes into close contact with the inner peripheral surface of the container P so as to seal it. In FIG. 5, reference numeral 2′ indicates a pump body.

A follow plate unit is proposed which includes a follow plate body, two keep plates, a bottom plate 4, and an annular seal made of elastic rubber. The bottom plate is identical in form with the plate body. One of the keep plates is fitted on the upper side of the main body. The other keep plate is fitted to the bottom plate. The annular seal is fixed to the keep plates. Only when the bottom plate comes into contact with the surface of the high-viscosity liquid in a drum, the weight of a pump and downward air pressure enlarge the outer diameter of the annular seal in comparison with the plate body and the bottom plate. In the process of fitting the follow plate unit into or taking it out of the drum, the weight of the plate body stretches the annular seal downward due to the elasticity of the seal, thereby reducing the outer diameter of the seal. While the pump, which is mounted on the top of the follow plate unit, is operating, the weight of the pump and downward air pressure enlarge the outer diameter of the annular seal. (Refer to Patent Document 1, for example) Patent Document 1: JP-H8-82282A (paragraphs 0005-0007 and FIGS. 1-3)

In a conventional method or apparatus as described above for pumping out the liquid contained in a container, the load of a pump etc. act on a follow plate. The seal around the follow plate is strong in sealing force to prevent liquid leakage. As a result, when the follow plate is moved vertically with the pump, the sliding resistance created by the contact between the seal and the inner peripheral surface of the container is high. For a similar reason, it is difficult for the follow plate to be lowered only by the load (weight) of the pump etc. Accordingly, it is often necessary to apply downward pressure forcedly to the follow plate by means of an air cylinder, a hydraulic cylinder, or the like. As stated already, it is necessary to position the follow plate concentrically in the container in order to prevent liquid leakage. Therefore, positioning is necessary when the container is put in the pumping apparatus. The positioning may require time and skill.

The present invention has been made in view of the foregoing points. The object of the present invention is to provide a method and an apparatus for pumping out the liquid in a container easily without any skill, and without liquid leaking between the inner peripheral surface of the container and the seal around a follow plate even if the sealing force of the seal is weakened.

In order to attain the foregoing object, a method according to the present invention for pumping out the high-viscosity or low-viscosity liquid contained in a container such as a pail includes the steps of inserting a follow plate into the container, lowering the follow plate by means of a lift, and starting to drive a pump, with the follow plate seated on the surface of the contained liquid and kept moving downward, and with the seal around the follow plate in contact with the inner peripheral surface of the container, the method being characterized in:

that, in consideration of the weight of the follow plate, the load of the pump, and the sealing force of the seal which acts on the inner peripheral surface of the container, the downward load of the follow plate is substantially balanced with the upward load exerted by a balance weight or the like; and

that the sealing force of the seal around the follow plate is reduced so that the plate can be lowered according to the amount of liquid pumped out by the self-sucking force of the pump.

The method according to the present invention makes it possible to reduce the sealing force of the seal. As a result, when the follow plate moves vertically, the sliding resistance of the inner peripheral surface of the container to it is low in comparison with the conventional methods. This enables the follow plate to move upward smoothly with relatively weak lifting force. This also enables the follow plate to move downward smoothly with the reaction caused by the sucking force of the pump, without applying additional downward load. The follow plate moves downward for a distance equivalent to the amount of liquid pumped from the container mainly by the self-sucking force of the pump. This prevents liquid leakage even if the sealing force is reduced. However, the sealing force needs to be set at such a value as to prevent air from being sucked between the seal and the inner peripheral surface of the container into the container by the sucking force of the pump. For a similar reason, liquid leakage hardly occurs even if the container is slightly eccentric from the follow plate. This makes it easy to position the container relative to the follow plate.

It is preferable to, as claimed in claim 2, so set the upward load that, with the follow plate seated on the surface of the liquid contained in the container, the weight of the follow plate does not lower the plate when the pump is not driven.

This prevents liquid leakage between the seal and the inner peripheral surface of the container even when the pump is stopped.

The sealing force may, as claimed in claim 3, be set to such a degree according to the property of the contained liquid that the seal can be in contact with the inner peripheral surface of the container or scrape off the liquid sticking to the surface. If the contained liquid is a low-viscosity liquid such as water, the sealing force may be weak to such a degree that the seal is only in contact with the inner peripheral surface. If the contained liquid is a high-viscosity liquid, the sealing force may be slightly strong to such a degree that the seal can scrape off the sticking liquid.

This minimizes the sliding resistance of the inner peripheral surface of the container to the follow plate moving vertically. The minimized resistance makes the vertical movement of the follow plate easy and smooth.

In order to attain the foregoing object, an apparatus according to the present invention for pumping out the liquid contained in a cylindrical or rectangular container open at the top thereof includes a circular or rectangular follow plate fitted around the suction port at the bottom of a pump, the apparatus being adapted to suck and pump out the contained liquid by driving the pump, with the follow plate inserted into the container and being lowered by a lift, the apparatus being characterized in:

that, in consideration of the weight of the follow plate, the load of the pump, and the sealing force of the seal which acts on the inner peripheral surface of the container, a balance weight is so fitted that an upward load for substantially balancing the downward load of the follow plate can act on the plate; and

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